References a manual listing for the current
element. See The href attribute for detailed information on supported values
and processing implications. If no
href is specified, processors can choose to generate
an appropriate listing for this element. All of
the book listings operate in a similar manner; for
example, <toc
href="toc.dita"/> references a topic
which contains a manual table of contents, while
<toc/> indicates that a
processor should generate the table of contents.